The present invention relates to a CVD reactor apparatus for forming CVD thin films on a substrate, and more particularly to a CVD reactor apparatus, suitable for thermal CVD, which can prevent thin films from being formed at portions other than a desired portion on a substrate to reduce the generation of deposition particles to thereby dispense with chamber cleaning, and which can therefore exhibit high throughput and high apparatus operating rate. Further, the present invention is concerned with a CVD reactor apparatus suitable for thermal CVD which can monitor only a reaction on the front of a substrate in a real time manner, can prevent a monitor unit from being damaged by chamber cleaning to permit a stable long-term monitoring operation without deterioration with time and is therefore easily applicable to automated operation to exhibit excellent productivity.
With advancement in high integration of LSI's, the LSI production process has required high-degree techniques. As for the problem that increasing difficulties are encountered in design of wiring for connection between an element and a wiring line or between wiring lines, for instance, the multilayer wiring technique has become indispensable for solving this problem. In this case, a method has been adopted in which, in order to connect lower wiring lines to upper wiring lines overlying the lower wiring lines through an intervening insulating film, fine or minute holes for conduction (hereinafter referred to as through-holes) are formed in the insulating film and the through-holes are filled with electrical conductors.
Methods for filling the through-holes have been known including methods capable of exhibiting good filling capability even when the through-hole diameter is very small. Of these methods, selective CVD (Chemical Vapor Deposition) of metal such as tungsten has been known as the most practical. The CVD of tungsten (hereinafter simply referred to as W) is classified into: a first type in which a film of high covering intimacy is deposited on the whole surface of a substrate through blanket deposition process and used, as it is, for wiring, and a second type in which only through-holes are filled through selective deposition process and a metal material of low resistivity such as Al (aluminum) is deposited to cover the whole surface. The following description will be given by way of the latter type.
Selective CVD of W is a method wherein a mixed gas of tungsten hexafluoride (WF6) and hydrogen (H.sub.2) or (SiH.sub.4) is introduced onto a specimen substrate heated to 250.degree. C. or more and contacted to the substrate to cause a W-film to grow on an undercoating metal (of aluminum, in this example) through any one of the following reactions: EQU WF6+2Al.fwdarw.W+2AlF.sub.3 EQU WF6+3H.sub.2 .fwdarw.W+6HF EQU 2WF6+3SiH.sub.4 .fwdarw.2W+3siF.sub.4 +3H.sub.2 (chemical formula 1).
As an example, a silicon wafer is used as the specimen substrate, an Al pattern is formed to provide an undercoating metal on the wafer surface, an insulating film of, for example, SiO.sub.2 is formed on the Al pattern and the insulating film is formed with through-holes to expose the undercoating metal.
In this case, a reaction pursuant to (chemical formula 1) does not take place on the insulating film of SiO.sub.2 but W selectively grows on only Al exposed to the inside of the through-holes to fill up the throughholes. A description relevant to this type of selective CVD of W is given in, for example, Journal of Electrochemical Society, Vol. 131 (1984), pp. 1427-1433 and "CVD Technique for VLSI", Report of the First Symposium of the ESC, Japan, 1988, pp. 48-65.
As prior art documents relevent to this kind of technique, one may refer to JP-A-64-17424, JP-A-4-226027, JP-A-4-233221, JP-A-4-268724 and JP-A-4-294526.
On the other hand, with recent advancement in LSI's, the plant investment cost has increased considerably and the production process grows, raising the production cost remarkably. To reduce the production cost, reduction of personnel expenses which results from automation is considered to be effective, and a monitoring technique, indispensable for automation, has been developed. A technique relevant to automation technology for LSI's is described in, for example, "Integrated Processing for Microelectronics Science and Technology", IBM Journal of Research and Development, Vol. 36 No. 2, (1992), p. 233.
The selective CVD method described previously is effective for the formation of fine and multilayer LSI wiring, but a problem is encountered in practicing this method. The problem resides in that selectivity in the aforementioned selective deposition is not always perfect and metal grows on the backside of the water. However, the formation of a film on the backside of the wafer is not desired. More particularly, a susceptor provided in a reactor and adapted to heat a wafer is heated to an equal or higher temperature than that of the wafer and hence a film is easily formed on the surface of the susceptor when CVD gas merely comes into contact therewith. In addition, since the backside of the wafer is not covered with an insulating film and an active silicon surface exposed to the backside, a deposition reaction proceeds when the gas contacts the silicon surface. The unwanted film thus formed has in general weak adhesiveness and is liable to peel off, causing the generation of particles and contaminants in a CVD reactor and inviting a reduction in the yield of the treatment process. Further, the problem of formation of the unwanted film is not inherent to the selective CVD and causes the generation of particles and contaminants in the CVD reactor also in blanket CVD, thus reducing the yield.
Therefore, it is becoming a common practice in the latest individual water processing type CVD equipment that every single wafer has its backside etched, backside, and/or that the inside wall of the cold-wall reactor is etched after every single deposition. Chamber cleaning inside the reactor performed before CVD is described in Conf. Proc. of Advanced Metallization for ULSI Applications (1991, N.J. and Tokyo; MRS), pp. 167-172 and 249-253.
However, wherein chamber cleaning inside the reactor is carried out before CVD, the chamber wall and especially such a heated portion as the susceptor are damaged by plasma, raising a new problem that particles resulting from decomposition and alteration, not deposition of the reactor constituent material are generated.
On the other hand, process monitoring techniques for performing automated unattended operation with a view of reducing the production cost have been developed as described previously and the application of a reaction gas monitor, mainly using a mass analyzer or a luminescence analyzer and a wafer temperature monitor using a pyro-thermometer, to the CVD process with which the present invention is concerned has been studied. In the conventional CVD reactor, however, film formation takes place at the wafer backside and unwanted portions inside the CVD reactor, making it difficult to accurately monitor reaction on the front side of the wafer (i.e., the element forming side of the wafer). Especially, in the selective CVD, since the reaction area on the wafer front is very small, and the amount of deposition reaction is far larger at the wafer backside and unwanted portions inside the CVD reactor than at the wafer front, monitoring the reaction on the wafer front is substantially impossible. Further, when a pyro-thermometer is used to monitor the wafer temperature, a quartz light guide and an IR (infrared) transparent window are generally used for transmission of infrared light to a detecting portion, as described in JP-A-4-130746. But, in the conventional CVD reactor, the light guide and the IR transparent window are damaged and deteriorated by plasma during chamber cleaning to gradually decrease the transmitivity for infrared light and monitoring of the wafer temperature becomes substantially impossible.